The invention relates to a reciprocating piston internal combustion engine having two adjacent cylinder banks with pistons movably disposed in the cylinders and having connecting rods for transmitting the movement of the pistons to a crankshaft.
The publication DE 43 12 954 A1 discloses such a reciprocating piston internal combustion engine, which is equipped with a device for variable compression of the mixture in the combustion chamber. The variable compression device comprises an upper connecting rod pivotally connected to the piston and to a lower cross lever, which is pivotally connected to a crankshaft. The connecting rod and the lower cross lever are connected to one another by a joint. A control lever, the position of which is variably adjustable, acts on a further joint on the cross lever. An adjustment of the position of the control lever also adjusts the point of articulation between the cross lever and the connecting rod. Different kinematic ratios with various top and bottom dead centers of the piston in the cylinder of the internal combustion engine can thereby be set, without the need to modify the design dimensions of the piston, the connecting rod or a crank pin on the crankshaft.
In order to vary the compression ratio, the casing-side point of articulation of the control lever must be at least capable of translatory displacement in the casing and the control lever must moreover be pivotally supported on the casing. In order to be able to displace the control lever, for adjustment of the compression ratio an additional mechanism is required.
It is the object of the invention to provide a compact reciprocating piston internal combustion engine having two banks of cylinders with adjustable compression ratios.
In a reciprocating internal combustion engine having first and second cylinder banks arranged adjacent each other so that the axes of their cylinders extend essential parallel, a crankshaft is rotatably supported between the longitudinal axes of the cylinders of the first and second cylinder banks and includes crank pins, on which cross levers are rotatably supported and piston rods connected with one of their ends to the pistons are rotatably supported with their other ends on the cross levers which have sidewardly extending portions that are controllably supported by control levers for adjusting the compression ratio in the cylinders of the engine.
The reciprocating piston internal combustion engine according to the invention combines the advantages of an internal combustion engine having two parallel banks of cylinders with the advantages of variable compression. The two banks of cylinders of the reciprocating piston internal combustion engine are arranged in relation to one another in such a way that the longitudinal axes of the cylinders in the first cylinder bank and second cylinder bank extend parallel or they enclose only a small angle, which is in particular less than 10xc2x0. The enclosed angle may be 5xc2x0, for example. With this at least approximately parallel arrangement of the two cylinder banks, a compact internal combustion engine of small overall dimensions is achieved, wherein the transverse dimensions, in particular, are less than those of a V-type internal combustion engines. The mechanism for the adjustment of the compression ratio comprises a cross-lever as a force transmitting member between the connecting rod and the crankshaft. This member is arranged transversely in relation to the longitudinal axis of the crankshaft. As a result, despite the approximately parallel alignment of the cylinders in the first and second cylinder bank, the connecting rods of each piston have are displaced by an adjustment of the transmission ratio only over a relatively small distance relative to the longitudinal cylinder axis for any adjustment position of the device for the adjustment of the transmission ratio. The lateral offset between cylinder longitudinal axis and crankshaft is bridged by means of the cross-lever.
It is furthermore proposed that the crankshaft is arranged in relation to the two cylinder banks in such a way that the longitudinal axis of the crankshaft lies between the longitudinal axes of the cylinders of the first and second cylinder bank. In particular, the crankshaft lies symmetrically or slightly asymmetrically below the first and second cylinder banks. In this arrangement the crankshaft is acted upon equally by the forces of the pistons of both cylinder banks, the power being transmitted between the connecting rods and the crankshaft via the cross levers.
Expediently, a cross lever is assigned to each piston of the internal combustion engine. In addition each cross lever is preferably connected to its own adjustable control lever. For this purpose the control lever is preferably pivotally connected to the cross lever on the side remote from the connecting rod. In this way each connecting rod can be supported essentially rectilinearly along the cylinder longitudinal axis and the reciprocating movement of the piston is performed symmetrically about the longitudinal axis of the cylinder, thereby avoiding a collision between the connecting rod and the cylinder inner walls. In addition this arrangement reduces the forces acting on the connecting rods and the pistons.
Immediately adjacent cylinders of the first and second cylinder banks may be slightly offset in the direction of the crankshaft longitudinal axis in order to avoid a collision between the cross levers assigned to the cylinders. This also makes it possible to provide two different crank pins on the crankshaft with different throw radii to the longitudinal axis of the crankshaft with or without intermediate webs, on which the cross levers of the immediately adjacent cylinders of the first and second cylinder banks are supported. The different throw radii mean that the kinematic lever ratios in the kinematic transmission path between connecting rod, cross lever and control lever between adjacent cylinders can be precisely adjusted to one another, particularly in the event that the control levers for the two cross levers of adjacent cylinders are situated on the same side of the internal combustion engine. This design affords the further advantage that all control levers can be adjusted by a common actuating member, for example by an eccenter shaft, which extends parallel to the crankshaft.
It may, however, also be expedient to couple the cross levers of adjacent cylinders with control levers disposed at opposite sides of the cylinder banks, an actuating member, in particular an eccentric shaft, being provided for each cylinder bank.
Other possible ways of adjusting the control levers may be considered as an alternative to an eccentric shaft. The control levers may also be actuated individually for example electrically, pneumatically or hydraulically. The use of template operating mechanisms is also possible.
Other advantages and suitable embodiments are set forth in the claims, the description of the drawings and the drawings.